1. Field of the Invention
This invention relates generally to orthopedic implants for use in orthopedic surgical. procedures and, more particularly, to cement molds for use in forming temporary orthopedic implants used in orthopedic surgical procedures.
2. Discussion of the Related Art
A natural joint may undergo degenerative changes due to a variety of etiologies. When these degenerative changes become so far advanced and irreversible, it may ultimately become necessary to replace the natural joint with a joint prosthesis. However, due to any number of reasons, a small portion of patients that undergo such orthopedic surgical procedures suffer from infections at the surgical site and generally around the implanted joint prosthesis. In order to cure such an infection in a two-stage reimplantation, the implanted joint prosthesis is generally removed, the site is thoroughly debrided and washed, antibiotics are applied to the infected site until the infection is eliminated, and a new revision type joint prosthesis is then implanted during a subsequent orthopedic surgical procedure. Systemic antibiotics may also act as an adjunct to local antibiotic delivery. Another technique, more popular in Europe, is the one stage reimplantation in which the prosthesis is removed, the site is debrided and washed and a new permanent implant is cemented in place using antibiotic loaded bone cement.
The currently available techniques for delivering the antibiotic to the infected joint area include mixing appropriate bone cement, such as (PMMA) poly-methyl-methacrylate, with an antibiotic, such as gentamicin, and applying the mixture to the infected joint area. Another technique involves the use of pre-loaded antibiotic cement beads which are retained on a string or wire. The antibiotic loaded bone cement is packed into the voids created by the explanted joint prosthesis while the joint is distended or the string of antibiotic loaded beads are dropped into the respective voids. During this period, the antibiotic leaches out from the bone cement and into the infected area, while the patient is unfortunately left substantially non-ambulatory or bed-ridden with very limited mobility. In addition, soft tissue contraction in the area about the joint may cause a more difficult revision surgery since the remaining bone portion is smaller than the explanted joint prosthesis. Moreover, the above techniques may also suffer from the disadvantage of sometimes being difficult or messy to use during the orthopedic surgical procedure. This disadvantage is primarily exhibited during the use of the antibiotic loaded bone cement in a doughy state and attempting to fill the appropriate region in the distended joint area.
In order to improve upon this technique, other techniques have involved the use of partial molds or casts in which the mixture of bone cement and antibiotic is packed into these partial molds by use of spoons or spatulas and left to harden. Once hardened, the brittle molds may be broken away and the bone cement, now resembling a joint prosthesis, is applied to the appropriate joint area. However, this technique also suffers from several disadvantages in that the partial molds or casts are made from a brittle material such that the molds are prone to fracturing or breaking before their use. Moreover, the molds are only partial molds in that only portions of the implant are formed and the molds generally have large exposed cavities such as two ends of a tube to receive the bone cement. This makes it extremely difficult to pack or load such molds with the antibiotic loaded bone cement. Furthermore, it is often times difficult to break away or remove these molds from the hardened bone cement.
Such disadvantages are also exhibited in U.S. Pat. Nos. 5,123,927 and 5,133,771 to Duncan, et al. in which a knee prosthesis and a hip prosthesis technique are disclosed. Here again, the disadvantages associated with the '927 and '771 patents are that they are somewhat clumsy and messy to work with. In other words, both the '927 and the '771 patents provide partial molds that are substantially open such that a rigid or hard bearing member is separately implanted into each of the molds to provide for an articulating temporary joint. Here again, however, the molds are filled manually by the use of spoons, spatulas, etc. and the molds do not provide a means for readily removing the molds once the antibiotic impregnated bone cement hardens. In addition, it appears that these molds are also reusable which requires the molds to be cleaned and sterilized before each use.
What is needed then is a cement mold to form a temporary implant which does not suffer from the above mentioned disadvantages. This, in turn, will provide a substantially completely sealed mold which may be filled in an automatic or controlled matter, provide a mold which may be readily handled and easily removed from the hardened bone cement, provide a mold that is easily tearable, provide a means to easily remove the mold from the formed temporary implant, reduce the amount of time a patient is bedridden, increase the efficiency of the surgical procedure while reducing the surgical time and cost, eliminating any recleaning or resterilizing, and create a repeatable procedure by providing a substantially fully enclosed and complete mold. It is, therefore, an object of the present invention to provide such a cement mold to form a temporary implant for use during an orthopedic surgical procedure.